In general, a letter envelope is used for sending a postal matter and letters, various bills, brochures, and advertising descriptions are put into the letter envelope in use.
Such a letter envelope is fabricated in various forms and provided with a window or an easy opening structure for the convenience of use.
Meanwhile, recently, as the Internet and smart phones become popular, people can simply and easily make communication or transceive information with other people, so the letter envelope is rarely used. Instead, the conventional letter envelopes are mainly used as direct marketing (DM) envelopes which are directly delivered to consumers or customers for the purpose of advertisement.
However, most of recipients who receive the DM envelopes used for the advertisement may discard the DM envelopes without opening the DM envelopes or after checking the advertisement at a glance, unless the recipients interest with the advertisement. For this reason, the desired advertisement effect is not expected from the DM envelopes.